"Associate SSO username to existing person": improve suggested GPG command

This bug concerns the following page: https://nm.debian.org/dm/claim

The suggested command on this page is the following:

gpg --fingerprint $YOUR_KEYID | sed -nre 's/Key fingerprint =//p'

There are multiple issues with this suggested command:

1. It is in the middle of a paragraph, so it is not easy to select and paste to a terminal;
2. If $LANG is not en, then the sed call will not be able to match the localized "Key fingerprint" translation; and
3. The sed command will list all fingerprints, from the main key to all of the subkeys — which makes it unclear what to paste in the key field (all fingerprints? the first one? the last one?).

I intent to propose a fix in a merge merge request in a moment that addresses this issue.